A wellhead housing may be located on the sea floor, so that a casing string may extend downward from the wellhead housing into the well, with the casing string supported in the wellhead housing by a casing hanger. A seal assembly may be installed between the casing hanger at the upper end of the casing string and the wellhead housing. The operator may install the casing string and seal assembly remotely, and in seas of considerable depths.
Running tools have been developed for delivering forces to set and test the downhole seal assemblies, as disclosed in U.S. Pat. No. 4,969,516. Hydraulic pressure may result in axial movement of a piston within a sealed hydraulic chamber in the running tool. Many hydraulically powered running tools are, however, complex and expensive. U.S. Pat. No. 5,044,442 discloses a hydraulic running tool which utilizes annulus pressure. Rams may be closed around a running string, creating a chamber below the rams. An elastomeric seal may be sealed to a portion of the running tool and to the wellhead. The seal and a collar enable pressure to be applied to stroke the tool. Fluid may be pumped downhole through choke and kill lines to set the casing hanger seal.
Other relevant patents include U.S. Pat. Nos. 4,757,860, 5,372,201, and 5,791,418. The '860 patent discloses a running tool for positioning a seal assembly between a casing hanger and a casing head. A first sleeve is connected to the hanger and a second sleeve is threadably connected to the first sleeve, and is movable between one position to support the seal assembly, and a second position for releasing the seal assembly to be lowered for sealing with the casing hanger. The '201 patent discloses a running tool which includes a pressure set seal, where the setting sleeve is sealed to the wellhead. The '418 patent discloses a tool designed to shift an external valve sleeve in a wellhead housing.
The disadvantage of the prior art are overcome by the present invention, and an improved annulus pressure actuated hanger seal assembly and running tool are hereinafter disclosed.